When recombinant attenuated Salmonella vaccines (RASV) are used to deliver heterologous antigens, it may be advantageous to reduce the host immune response against the RASV carrier, thereby enhancing the immune response against the heterologous antigen. The dominant immunogen on the Salmonella cell surface is lipopolysaccharide (LPS) O-antigen. However, strains with mutations that eliminate LPS O-antigen may be less immunogenic due to failure of these kinds of mutants to colonize the intestinal tract and invade intestinal mucosal cells. Hence, there is a need in the art for a bacterium that comprises a mutation that allows O-antigen synthesis, yet still reduces the host immune response against the bacterium. This feature would also contribute to the potential use of the RASV vector for multiple vaccines to prevent against multiple infectious disease agents.